18 research outputs found
Increasing the raw contrast of VLT/SPHERE with the dark-hole technique. II. On-sky wavefront correction and coherent differential imaging
Context. Direct imaging of exoplanets takes advantage of state-of-the-art
adaptive optics (AO) systems, coronagraphy, and post-processing techniques.
Coronagraphs attenuate starlight to mitigate the unfavorable flux ratio between
an exoplanet and its host star. AO systems provide diffraction-limited images
of point sources and minimize optical aberrations that would cause starlight to
leak through coronagraphs. Post-processing techniques then estimate and remove
residual stellar speckles such as noncommon path aberrations (NCPAs) and
diffraction from telescope obscurations. Aims. We aim to demonstrate an
efficient method to minimize the speckle intensity due to NCPAs during an
observing night on VLT/SPHERE. Methods. We implement an iterative dark-hole
(DH) algorithm to remove stellar speckles on-sky before a science observation.
It uses a pair-wise probing estimator and a controller based on electric field
conjugation. This work presents the first such on-sky minimization of speckles
with a DH technique on SPHERE. Results. We show the standard deviation of the
normalized intensity in the raw images is reduced by a factor of up to 5 in the
corrected region with respect to the current calibration strategy under median
conditions for VLT. This level of contrast performance obtained with only 1 min
of exposure time reaches median performances on SPHERE that use post-processing
methods requiring 1h-long sequences of observations. We also present an
alternative calibration method that takes advantage of the starlight coherence
and improves the post-processed contrast levels rms by a factor of about 3.
Conclusions. This on-sky demonstration represents a decisive milestone for the
future design, development, and observing strategy of the next generation of
ground-based exoplanet imagers for 10m to 40m telescope.Comment: Accepted in Astronomy & Astrophysic
Experimental comparison of model-free and model-based dark hole algorithms for future space telescopes
Coronagraphic instruments provide a great chance of enabling high contrast
spectroscopy for the pursuit of finding a habitable world. Future space
telescope coronagraph instruments require high performing focal plane masks in
combination with precise wavefront sensing and control techniques to achieve
dark holes for planet detection. Several wavefront control algorithms have been
developed in recent years that might vary in performance depending on the
coronagraph they are paired with. This study compares 3 model-free and
model-based algorithms when coupled with either a Vector (VVC) or a Scalar
(SVC) Vortex Coronagraph mask in the same laboratory conditions: Pairwise
Probing with Electric Field Conjugation, the Self-Coherent Camera with Electric
Field Conjugation, and Implicit Electric Field Conjugation. We present
experimental results from the In-Air Coronagraph Testbed (IACT) at JPL in
narrowband and broadband light, comparing the pros and cons of each of these
wavefront sensing and control algorithms with respect to their potential for
future space telescopes.Comment: Conference Proceedings of SPIE: Techniques and Instrumentation for
Detection of Exoplanets XI, vol. 12680 (2023
Laboratory demonstration of the triple-grating vector vortex coronagraph
The future Habitable Worlds Observatory aims to characterize the atmospheres
of rocky exoplanets around solar-type stars. The vector vortex coronagraph
(VVC) is a main candidate to reach the required contrast of .
However, the VVC requires polarization filtering and every observing band
requires a different VVC. The triple-grating vector vortex coronagraph (tgVVC)
aims to mitigate these limitations by combining multiple gratings that minimize
the polarization leakage over a large spectral bandwidth. In this paper, we
present laboratory results of a tgVVC prototype using the In-Air Coronagraphic
Testbed (IACT) facility at NASA's Jet Propulsion Laboratory and the Space
Coronagraph Optical Bench (SCoOB) at the University of Arizona Space
Astrophysics Lab (UASAL). We study the coronagraphic performance with
polarization filtering at 633 nm and reach a similar average contrast of between 3-18 at the IACT, and
between 3-14 at SCoOB. We explore the limitations of the tgVVC by
comparing the testbed results. We report on other manufacturing errors and ways
to mitigate their impact.Comment: 9 pages, 5 figures, SPIE Optics + Photonics - Techniques and
Instrumentation for Detection of Exoplanets X
Adaptive optics performance of a simulated coronagraph instrument on a large, segmented space telescope in steady state
Directly imaging Earth-like exoplanets (``exoEarths'') with a coronagraph
instrument on a space telescope requires a stable wavefront with optical path
differences limited to tens of picometers RMS during exposure times of a few
hours. While the structural dynamics of a segmented mirror can be directly
stabilized with telescope metrology, another possibility is to use a
closed-loop wavefront sensing and control system in the coronagraph instrument
that operates during the science exposures to actively correct the wavefront
and relax the constraints on the stability of the telescope. In this paper, we
present simulations of the temporal filtering provided using the example of
LUVOIR-A, a 15~m segmented telescope concept. Assuming steady-state aberrations
based on a finite element model of the telescope structure, we (1)~optimize the
system to minimize the wavefront residuals, (2)~ use an end-to-end numerical
propagation model to estimate the residual starlight intensity at the science
detector, and (3)~predict the number of exoEarth candidates detected during the
mission. We show that telescope dynamic errors of 100~pm~RMS can be reduced
down to 30~pm~RMS with a magnitude 0 star, improving the contrast performance
by a factor of 15. In scenarios where vibration frequencies are too fast for a
system that uses natural guide stars, laser sources can increase the flux at
the wavefront sensor to increase the servo-loop frequency and mitigate the high
temporal frequency wavefront errors. For example, an external laser with an
effective magnitude of -4 allows the wavefront from a telescope with 100~pm~RMS
dynamic errors and strong vibrations as fast as 16~Hz to be stabilized with
residual errors of 10~pm~RMS thereby increasing the number of detected planets
by at least a factor of 4.Comment: Published in JATIS. arXiv admin note: substantial text overlap with
arXiv:2108.0640
Comparison of focal plane wavefront sensing technics dedicated to space missions for the direct imaging and spectroscopy of exoplanets
Comprendre la formation, l'évolution et la surprenante diversité des planètes extrasolaires est un des grands enjeux de l'astrophysique moderne. En deux décennies, de nombreuses découvertes ont déjà révélé la nature complexe de plus de 4000 objets. Pourtant, on connaît peu de choses sur l'atmosphère de ces planètes alors qu’il s’agit d’un point crucial pour déterminer les conditions d'apparition de la vie ailleurs que sur Terre. L'imagerie directe est une technique appropriée à l'étude spectrale des atmosphères d'exoplanètes similaires à celles du Système Solaire.L'imagerie des exoplanètes est cependant limitée par le très grand contraste et par la proximité entre exoplanètes et étoiles. Des techniques optimisées pour l'imagerie à très haute dynamique telles que la coronographie sont donc indispensables. Les coronographes atténuent la lumière des étoiles sans affecter le signal provenant de leurs environnements proches pour le révéler. Cependant, la turbulence atmosphérique, ainsi que les défauts de polissage, les erreurs d'alignement et les dilatations thermiques des télescopes qui peuvent varier avec le temps limitent encore leurs performances. Des techniques de correction active d'aberrations composées de miroirs déformables et d'analyseurs de front d'onde équiperont alors les futurs instruments haute-dynamiques tels que les projets spatiaux WFIRST, HaBEX ou LUVOIR ou encore les instruments aux foyers des Extremely Large telescopes.L'instrument Très Haute Dynamique 2 (THD2) situé à l'Observatoire de Paris/LESIA est un banc de test dédié à ce type d'activité. Durant cette thèse, plusieurs algorithmes d'analyse et de contrôle du front d'onde développés par différentes équipes en Europe et aux États-Unis ont été testés et comparés dans les mêmes conditions de stabilité sur le THD2. Lors de ces tests, la technique d'analyse pair-wise associée à une technique de conjugaison du champ électrique a d'ailleurs démontré d'excellentes performances en contraste dans des conditions spatiales, sans aucune modification du design optique de l'instrument. Fort de cette expérience, cette méthode a alors été implémentée sur l'instrument haute-dynamique VLT/SPHERE dont les résultats sur source interne laissent entrevoir des améliorations en contraste de plusieurs ordres de grandeur.Understanding the formation, the evolution and the diversity of extrasolar planets is an important purpose in modern astrophysics. More than 4,000 objects have been discovered since the first discovery of an exoplanet orbiting a solar-type star in 1995. Knowledge about atmospheres of these planets is crucial to determine the conditions for the appearance of life. However, it remains unknown while direct imaging technique would be a powerfull technique to study their spectra.Exoplanet imaging is limited by the large contrast and the small distance which exists between exoplanets and stars. Techniques optimized for high-contrast imaging such as coronography are therefore essential. Coronographs attenuate the light of stars without affecting the fait signal of their circumstellar environments. However, atmospheric turbulence, as well as polishing defects, alignment errors and thermal expansions of telescopes which can vary over time still limit their performance. Techniques dedicated to active correction of aberrations relied on deformable mirrors and wavefront sensors will equip future high-contrast imaging facilities such as WFIRST, HaBEX or LUVOIR spacecrafts or the Extremely Large telescopes.The instrument Très Haute Dynamique 2 (THD2) located at Observatoire de Paris/LESIA is a testbed dedicated to such projects. During this PhD, several wavefront sensor and control algorithms, originally developed by different teams in Europe and the United-States, were tested and compared under the same environmental conditions on the THD2. During these tests, the pair-wise sensor combined with an electric field conjugation technique has also demonstrated excellent contrast performance under spatial conditions, without any modification of the instrument optical path. This method was then implemented on the high-contrast VLT/SPHERE instrument in which we performed improvements in contrast of several orders of magnitude with the calibration unit
Comparaison des techniques d’analyse de surface d’onde en plan focal dédiées aux missions spatiales d’imagerie directe et de spectroscopie des planètes extrasolaires
Understanding the formation, the evolution and the diversity of extrasolar planets is an important purpose in modern astrophysics. More than 4,000 objects have been discovered since the first discovery of an exoplanet orbiting a solar-type star in 1995. Knowledge about atmospheres of these planets is crucial to determine the conditions for the appearance of life. However, it remains unknown while direct imaging technique would be a powerfull technique to study their spectra.Exoplanet imaging is limited by the large contrast and the small distance which exists between exoplanets and stars. Techniques optimized for high-contrast imaging such as coronography are therefore essential. Coronographs attenuate the light of stars without affecting the fait signal of their circumstellar environments. However, atmospheric turbulence, as well as polishing defects, alignment errors and thermal expansions of telescopes which can vary over time still limit their performance. Techniques dedicated to active correction of aberrations relied on deformable mirrors and wavefront sensors will equip future high-contrast imaging facilities such as WFIRST, HaBEX or LUVOIR spacecrafts or the Extremely Large telescopes.The instrument Très Haute Dynamique 2 (THD2) located at Observatoire de Paris/LESIA is a testbed dedicated to such projects. During this PhD, several wavefront sensor and control algorithms, originally developed by different teams in Europe and the United-States, were tested and compared under the same environmental conditions on the THD2. During these tests, the pair-wise sensor combined with an electric field conjugation technique has also demonstrated excellent contrast performance under spatial conditions, without any modification of the instrument optical path. This method was then implemented on the high-contrast VLT/SPHERE instrument in which we performed improvements in contrast of several orders of magnitude with the calibration unit.Comprendre la formation, l'évolution et la surprenante diversité des planètes extrasolaires est un des grands enjeux de l'astrophysique moderne. En deux décennies, de nombreuses découvertes ont déjà révélé la nature complexe de plus de 4000 objets. Pourtant, on connaît peu de choses sur l'atmosphère de ces planètes alors qu’il s’agit d’un point crucial pour déterminer les conditions d'apparition de la vie ailleurs que sur Terre. L'imagerie directe est une technique appropriée à l'étude spectrale des atmosphères d'exoplanètes similaires à celles du Système Solaire.L'imagerie des exoplanètes est cependant limitée par le très grand contraste et par la proximité entre exoplanètes et étoiles. Des techniques optimisées pour l'imagerie à très haute dynamique telles que la coronographie sont donc indispensables. Les coronographes atténuent la lumière des étoiles sans affecter le signal provenant de leurs environnements proches pour le révéler. Cependant, la turbulence atmosphérique, ainsi que les défauts de polissage, les erreurs d'alignement et les dilatations thermiques des télescopes qui peuvent varier avec le temps limitent encore leurs performances. Des techniques de correction active d'aberrations composées de miroirs déformables et d'analyseurs de front d'onde équiperont alors les futurs instruments haute-dynamiques tels que les projets spatiaux WFIRST, HaBEX ou LUVOIR ou encore les instruments aux foyers des Extremely Large telescopes.L'instrument Très Haute Dynamique 2 (THD2) situé à l'Observatoire de Paris/LESIA est un banc de test dédié à ce type d'activité. Durant cette thèse, plusieurs algorithmes d'analyse et de contrôle du front d'onde développés par différentes équipes en Europe et aux États-Unis ont été testés et comparés dans les mêmes conditions de stabilité sur le THD2. Lors de ces tests, la technique d'analyse pair-wise associée à une technique de conjugaison du champ électrique a d'ailleurs démontré d'excellentes performances en contraste dans des conditions spatiales, sans aucune modification du design optique de l'instrument. Fort de cette expérience, cette méthode a alors été implémentée sur l'instrument haute-dynamique VLT/SPHERE dont les résultats sur source interne laissent entrevoir des améliorations en contraste de plusieurs ordres de grandeur
Exoplanet direct imaging in ground-based conditions on THD2 bench
International audienceThe next generation of ground-based instruments aims to break through the knowledge we have on exoplanets by imaging circumstellar environments always closer to the stars. However, direct imaging requires an AO system and high-contrast techniques like a coronagraph to reject the diffracted light of an observed star and an additional wavefront sensor to control quasi-static aberrations, including the non common path aberrations. To observe faint objects, a focal plane wavefront sensor with a sub-nanometric wavefront control capability is required. In the past few years, we developed the THD2 bench which is a testbed for high-contrast imaging techniques, working in visible and near infrared wavelengths and currently reaching contrast levels lower than 1e-8 under space-like simulated conditions. We recently added a turbulence wheel on the optical path which simulates the residuals given by a typical extreme adaptive optics system and we tested several ways to remove quasi-statics speckles. One way to estimate the aberrations is a method called pair-wise probing where we record few images with known-shapes we apply on the adaptive optics deformable mirror. Once estimated, we seek to minimize the focal-plane electric field by an algorithm called Electric Field Conjugation. In this paper, we present the first results obtained on the THD2 bench using these two techniques together in turbulent conditions. We then compare the achieved performance with the one expected when all the quasi-static speckles are corrected
Exoplanet direct imaging in ground-based conditions on THD2 bench
International audienceThe next generation of ground-based instruments aims to break through the knowledge we have on exoplanets by imaging circumstellar environments always closer to the stars. However, direct imaging requires an AO system and high-contrast techniques like a coronagraph to reject the diffracted light of an observed star and an additional wavefront sensor to control quasi-static aberrations, including the non common path aberrations. To observe faint objects, a focal plane wavefront sensor with a sub-nanometric wavefront control capability is required. In the past few years, we developed the THD2 bench which is a testbed for high-contrast imaging techniques, working in visible and near infrared wavelengths and currently reaching contrast levels lower than 1e-8 under space-like simulated conditions. We recently added a turbulence wheel on the optical path which simulates the residuals given by a typical extreme adaptive optics system and we tested several ways to remove quasi-statics speckles. One way to estimate the aberrations is a method called pair-wise probing where we record few images with known-shapes we apply on the adaptive optics deformable mirror. Once estimated, we seek to minimize the focal-plane electric field by an algorithm called Electric Field Conjugation. In this paper, we present the first results obtained on the THD2 bench using these two techniques together in turbulent conditions. We then compare the achieved performance with the one expected when all the quasi-static speckles are corrected
Optimization and performance of multi-deformable mirror correction on the THD2 bench
International audienceHigh-contrast imaging (HCI) techniques appear like the best solutions to directly characterize the atmosphere of large orbit planets and planetary environments. In the last 20 years, different HCI solutions have been proposed based on coronagraphs. Some of them have been characterized in the laboratory or even on the sky. The optimized performance of these coronagraphs requires a perfect wavefront unreachable without active control of the complete electrical field (phase and amplitude) at the entrance of the instrument. While the correction of the phase aberrations is straight forward using deformable mirrors (DM), correcting amplitude defects is complex and still under study at the laboratory level. The next generation of HCI instrument either for ground-based (PCS instrument for ELT) or space-based (LUVOIR, HabEx) telescopes will require a practical and operational solution for amplitude corrections. The implementation of a DM located at a finite distance from the pupil is a simple solution that has been chosen by most of the projects. There have been only a few investigations on the optimization of the mirror positions for dedicated optical designs. In this paper, we give an intuitive approach that helps defining the best deformable mirror position in an instrument. Then, we describe its application to the THD2 and the performance in the laboratory that reaches a contrast level below 10<SUP>-8</SUP> at distance larger than 6 lambda/D